On Monday, the general secretary of ASLEF, Mick Whelan, hit out at government plans to reform strike laws.

The proposal would see a 50% turnout required for an industrial action ballot, and in core public services 40% would have to back strike action.

"It smacks of Germany in the 1930s when trade union leaders, and activists, were rounded up, and imprisoned, and, in some cases, executed," Whelan said. "The Nazis banned unions, and strikes, in 1933 and that is what the Tories are trying to do now. They want to effectively neuter the unions – the only part of civil society now able to fight back – in Britain."

There are more talks due on Tuesday to try to avert next month's strike.

The Rail, Maritime and Transport (RMT) and Unite unions have said their members will also join the proposed strike on 5 August.

RMT’s general secretary, Mick Cash, said in a statement: "The unity and determination of staff across London underground in the dispute ‎over night tube, the imposition of the rosters from hell and the destruction of any semblance of work/life balance remains rock solid.

"Workers in all grades are furious at the attempt to rip up long-standing agreements in an effort to bulldoze through these wholly unacceptable new working patterns."

He added: "RMT also remains in dispute over the parallel issue of the axing of 850 station staff jobs, cuts which make a mockery of the safe delivery of the night tube in just a few weeks time.

"RMT remains available for talks and tube managers need to understand the universal anger of their staff if we are to start making some serious progress in negotiations."